Analysis of common problems and relevant standards

2022-08-09
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Analysis of common problems of composite aluminized film and related standards

aluminized composite film is a kind of soft packaging material with "aluminum luster" and good barrier, which is formed by compounding aluminized film (generally VMPET, vmbopp, VMCPP or vmpe, of which VMPET and VMCPP are the most commonly used) with transparent plastic film. It has been widely used in the outer packaging of food, health products, medicine and cosmetics, especially in dry and expanded food, It has been widely used because of its very good metallic luster, convenience, low price and good barrier performance (compared with that before aluminum plating). However, in our investigation, we found that the composite condition of aluminized composite film on the market is worrying, and there are two common problems: serious white spot phenomenon and low peel strength. Especially in the composite film products with pet/vmcpp and pet/vmpet/pe structures. Here we analyze the causes and Countermeasures of the above problems in dry compounding, and hope to communicate with friends

causes and solutions of white spot phenomenon

the white spot phenomenon of composite aluminized film can be described in this way. There are obvious white spots on the performance of the composite product, which can be randomly distributed and uneven in size. There are two cases, one is: it occurs when getting off the machine, but it basically disappears after ripening; The other is: it occurs when getting off the machine and does not disappear after ripening. The latter is the biggest problem that affects the appearance. Such spots are most likely to appear on the effect of printing with a full white background or a light background. In fact, it should be said that as long as such white spots appear, they are generally full version (except for equipment reasons). It's just that white and light background have poor hiding power, which is easy to see. There are many reasons for the phenomenon of white spots, mainly due to three reasons:

1. The ink has a large particle bottom or a wide particle size distribution, and generally the particle size of white ink has a greater impact. Ethyl ester in the adhesive is a good solvent for ink. The results of soaking ink particles with different particle sizes are different. The chromaticity changes after drying in the oven will be different, which looks like "white spots". Generally, in this case, it is obvious when getting off the machine, and the white dot phenomenon will be reduced and may disappear after ripening

2. The surface tension of the adhesive is high, and the effect of infiltration and spreading on the aluminized film is poor. This is a main reason for the "white spot phenomenon" of aluminum coating at present. The coating effect of adhesive is not good. After the printing layer is covered, the color of different parts will change, producing the same effect as before, and sometimes producing large spots

3. Equipment and process reasons. On the one hand, the workers are not aware of the particularity of aluminum coating composite, which has its unique place; On the other hand, the problems of equipment drying, coating and the system itself cannot ensure the full and uniform coating of adhesive or the full volatilization of ethyl ester

there are other reasons, such as the roller grain of the full bottom printing line is too shallow, which reduces the ink coverage, etc

white spots can be eliminated by taking the following measures:

1. Increase the particle size detection index of different batches of inks and strictly control it, especially if the particle size and particle size distribution of full bottom inks are outside the standard range; Choose excellent and stable suppliers

2. Special adhesive for aluminizing film is used. The surface tension of the special adhesive for aluminized film composite is low, and the coating and spreading effect on the surface of aluminized layer is significantly better than that of general-purpose adhesive. Using aluminized glue will be very easy to control the leveling of glue liquid, and have a better coating state. In terms of the adhesive coating state alone, the use of aluminized adhesive can eliminate the possibility of white spots

3. There is a certain matching relationship between the viscosity of the glue solution and the number of lines in the line roll. If the matching range is exceeded too much, the coating state of the glue will be destroyed, resulting in the generation of "white spots", which is more of concern

4. Adopt aluminized film gluing method. The commonly used coating process is the coating of printing film (ink surface). Here, a special coating method is used to avoid the uneven penetration of ethyl ester into the ink layer and the uneven penetration of ethyl ester into the ink layer. At the same time, the coated adhesive can fully and evenly cover the surface of the aluminum layer, which can well eliminate white spots. However, this process has its great limitations. First, it is limited to the compounding of VMPET, and other aluminized films will be stretched and deformed under the effect of tension due to the heating in the oven; Secondly, a certain peel strength will be sacrificed

5. Flexible packaging enterprises must adhere to the regular cleaning system of coating rollers and master the correct cleaning methods of coating rollers. When producing full white background or light background printing film, we should pay attention to two points. First, thoroughly clean the scraper, coating roller, flattening roller, etc. before production

6. Thoroughly dry the adhesive. Due to the good barrier property of aluminum plating, if the bonding in the composite film is not completely dry, then a large amount of residual solvent needs to be released quickly after the composite film enters the curing room, and bubbles are bound to form under the barrier of aluminum plating film. Even there will be no white spots when getting off the machine, but there will be white spots after ripening

standard of composite aluminum coating and peel strength of composite aluminum coating

we often use ordinary tape to check the adhesion of aluminum coating before aluminum coating. The order quantity of blow molding machine will reach a new height. In the peel test of aluminum coating/tape, the aluminum coating of aluminum coating will not be peeled off, and the peel strength of aluminum coating/tape at this time is ≥ 2.0n/15mm; After compounding the aluminized film with other films, the peel strength of the aluminized surface of the composite film decreases sharply after aging, and most of the aluminized surface will be completely or partially transferred. At this time, the peel strength of the aluminized layer should preferably reach about 0.6n/15mm, generally 0 3n/15mm, or even lower. If the aluminized film migrates, the vacuumized aluminized film packaging (such as tea packaging) will migrate over time, resulting in large bubbles; If it is a jelly cover, when it is removed, it will only uncover the upper layer, and there is still no jelly to eat

some qualified enterprises have done such tests. If imported aluminized film is selected and the above tests are repeated, the results will be completely different. The strength of aluminized layer of aluminized composite film is still very high, and there is no problem of aluminized layer migration

through the above analysis, the migration of aluminum plating layer has a great relationship with the quality of aluminum plating itself, because there is a great difference in quality between domestic aluminum plating film and imported aluminum plating film. Imported aluminum plating film is aluminum plating film with primer, while domestic aluminum plating generally has no primer

due to the current situation of domestic aluminum plating film, the reality of plating migration generally exists in the industry. Although the number of aluminum plating composite films used is huge, and the production of aluminum plating composite film products has a history of more than 20 years, so far, there are still no relevant general industry standards and enterprise standards for aluminum plating film and aluminum plating composite film. At present, only a few industry standards and enterprise standards mention the peel strength of aluminized composite film. For example, in YY "composite film for pharmaceutical packaging", the composite film is classified into Ⅲ plastic and aluminized film according to the material combination. The example structures are opp/vmcpp and pet/vmpet/pe. In terms of strength requirements, double-layer composite ≥ 1.0n/15mm, inner layer and sub inner layer ≥ 2.5n/15mm. From the above standards, it can be seen that the strength requirement of opp/vmcpp is ≥ 1.0n/15mm, while at present, a large part of products in the market still fail to meet the standard. In the structure of pet/vmpet/pe, only the strength of the inner layer and the sub inner layer (vmpet/pe) is mentioned, but the strength of the outer layer and the sub inner layer (pet/vmpet) is not mentioned, which is also to avoid the common problems in the current market. If the standard of aluminized composite film is formulated according to the current low level, the user cannot connect the end, Xiaoping thinks it is acceptable; If the fixed price is too high, the flexible packaging enterprises cannot reach it

at present, when many enterprises sign contracts, in the column of implementation standards, most of them write the column of implementation of relevant national or industrial standards, and most of them write the column of implementation of relevant national or unemployed standards. At present, this standard should be empty. This has caused the embarrassing situation that there is no standard implementation between the supplier and the demander, and also caused the problem that it is difficult to straighten out the acceptance and complaints of both parties

fortunately, at present, many enterprises have made a lot of efforts in solving the migration of aluminum coating, and have made a lot of achievements. For example, Beijing GAOMENG Chemical Co., Ltd. has successively launched the first generation of aluminum coating adhesive yh501s (50%), the second generation of aluminum coating adhesive yh501s (75%), and the third generation of aluminum coating adhesive yh501sl. It has made outstanding contributions to effectively alleviate the migration of domestic aluminum coating during lamination and improve the peel strength of aluminum coating

we can see a phenomenon when we do the stripping test of aluminum coating. Do everything possible to make partners and entrepreneurial platforms' fall in love 'bad usually occurs in the aluminized layer pet (CPP) interface, and only when most of the aluminized layer is transferred, the peel strength will be significantly reduced. For detailed discussion, please refer to the article "Application of yh501s on pet/vmcpp composite film" published in the 4th issue of plastic packaging in 2000, which has a detailed discussion on the influence of composite peel strength of aluminized film. The conclusion is that the peel strength of aluminum coated composite adhesive will be greatly improved. Here, I only introduce to my friends the production experience of improving composite peel strength for a few years for their reference

1. Select appropriate VMCPP and VMPET. At present, the prices of aluminized films from different manufacturers are almost the same. Using well-known brand products, the coating adhesion fastness is more guaranteed, thus ensuring the necessary conditions for high peel strength

2. Establish a set of testing methods for the adhesion fastness of coatings, so as to know the adhesion fastness of VM film coatings in different batches, which can ensure the stability of product quality in different batches

3. The composite fastness can be improved by reducing the temperature of the composite roller. The negative effect is that the glue coating state is relatively poor. In addition, the initial peel strength becomes worse after just getting off the machine

4. Adopt a special method, that is, when applying VMPET glue, try to reduce the oven temperature and increase ventilation. The negative effect is that the volatility of ethyl ester is affected. The residue of ethyl ester increased. The manufacturer should consider the ventilation condition of the equipment, compare the degree to which the temperature is reduced, and whether the ethyl ester can volatilize more fully

5. For pet/vmpet/pe (CPP) structure, the first composite will not enter the curing room, and the second composite will be carried out after hours in the workshop, and the composite strength will be improved to a certain extent

6. For pet/vmpet/pe (CPP) structure, when PE thickness is greater than 50 μ Or CPP thickness is greater than 40 μ It is suggested to carry out a small test to adjust the best working state to ensure that the peel strength meets the design requirements

7. Appropriately reducing the curing dose can also improve the peel strength, which is generally not less than 15% of the normal amount. Otherwise, the curing problem of the adhesive will occur

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